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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7230) Support rolling downgrade
Date Tue, 14 Oct 2014 01:10:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14170329#comment-14170329
] 

Tsz Wo Nicholas Sze commented on HDFS-7230:
-------------------------------------------

Here is the Rolling Downgrade procedure.  Suppose a rolling upgrade is in progress in a a
HA cluster.
# Downgrade DNs
## Choose a small subset of datanodes (e.g. all datanodes under a particular rack).
### Run "hdfs dfsadmin -shutdownDatanode <DATANODE_HOST:IPC_PORT> upgrade" to shutdown
one of the chosen datanodes.
### Run "hdfs dfsadmin -getDatanodeInfo <DATANODE_HOST:IPC_PORT>" to check and wait
for the datanode to shutdown.
### Downgrade and restart the datanode.
### Perform the above steps for all the chosen datanodes in the subset in parallel.
## Repeat the above steps until all datanodes in the cluster are downgraded.
# Downgrade Active and Standby NNs: NN1 is active and NN2 is standby.
## Shutdown and downgrade NN2.
## Start NN2 as standby (the “-rollingUpgrade downgrade” option is not needed)
## Failover from NN1 to NN2 so that NN2 becomes active and NN1 becomes standby.
## Shutdown and downgrade NN1.
## Start NN1 as standby (the “-rollingUpgrade downgrade” option is not needed).
# Finalize
## Run "hdfs dfsadmin -rollingUpgrade finalize" to finalize the procedure.


> Support rolling downgrade
> -------------------------
>
>                 Key: HDFS-7230
>                 URL: https://issues.apache.org/jira/browse/HDFS-7230
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Tsz Wo Nicholas Sze
>
> HDFS-5535 made a lot of improvement on rolling upgrade.  It also added the cluster downgrade
feature.  However, the downgrade described in HDFS-5535 requires cluster downtime.  In this
JIRA, we discuss how to do rolling downgrade, i.e. downgrade without downtime.



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